Spring的方法注入

晨曦之光 发布于 2012/04/25 16:18
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当一个Bean依赖的Bean和自己生命周期不同的时候:如Bean A依赖Bean B,Bean A 是singleton,如果需要在Bean A每次用到Bean B的时候都用一个Bean B的新的实例,通过在配置文件中通过 property或者 contructor-arg是不能实现的.这时候只能在Bean A中用Bean B的时候动态得到.通常的做法有两种:

1,Bean A实现 ApplicationContextAware, Spring初始化的时候会将 ApplicationContext 传给Bean A,Bean A通过getBean("BeanB")方法每次得到Bean B.("BeanB"最好不要hardcode,通过property传入)例:

public class ContextAwareBean implements ApplicationContextAware {
    protected static final Log log = LogFactory.getLog(AnotherBean.class);
    private String anotherBeanName;
    private ApplicationContext applicationContext;
   
    public String getAnotherBeanName() {
        return anotherBeanName;
    }
    public void setAnotherBeanName(String anotherBeanName) {
        this.anotherBeanName = anotherBeanName;
    }
    public void process() {
        log.info("process applicationContext " + applicationContext);
        AnotherBean anotherBean = createAnotheBean();
        anotherBean.doSth();
       
    }
    protected AnotherBean createAnotheBean() {
   
    return this.applicationContext.getBean(anotherBeanName, AnotherBean.class);
    }
    public void setApplicationContext(ApplicationContext applicationContext){
        log.info("setApplicationContext " + applicationContext);
        this.applicationContext = applicationContext;
    }
}
 public class AnotherBean {
    protected static final Log log = LogFactory.getLog(AnotherBean.class);
    public String doSth(){
        log.info("AnotherBean.doSth");
        return "do something";
    }
}

<bean id="AnotherBean" class="com.test.spring.di.mtddi.AnotherBean"  scope="prototype"/>
   
    <bean id="ContextAwareBean" class="com.test.spring.di.mtddi.ContextAwareBean" >
        <property name="anotherBeanName" value="AnotherBean"/>
    </bean>
2,方法注入:在Bean A中定义一个方法,返回类型是Bean B,在配置文件中通过"lookup-method"告诉Spring动态覆盖该方法,并返回Bean B的一个实例:

public  abstract class ReplacedBean {
protected static final Log log = LogFactory.getLog(ReplacedBean.class);
   
    public void process() {
       
        AnotherBean anotherBean = createAnotheBean();
        anotherBean.doSth();
       
    }
    protected abstract AnotherBean createAnotheBean();
   
}

<bean id="AnotherBean" class="com.test.spring.di.mtddi.AnotherBean"  scope="prototype"/>

<bean id="ReplacedBean" class="com.test.spring.di.mtddi.ReplacedBean" >
        <lookup-method name="createAnotheBean" bean="AnotherBean"/>
    </bean>
客户端代码:
public class MtddiClient {
    private static BeanFactory factory;
    private static ApplicationContext ctx;
    static {
        Resource resource = new ClassPathResource("conf/mtddiAppcontext.xml");
        factory = new XmlBeanFactory(resource);
       
        ctx = new ClassPathXmlApplicationContext("conf/mtddiAppcontext.xml");
    }
    /**
     * @param args
     */
    public static void main(String[] args) {
        /*不能通过bean factory的方式得到bean
        ContextAwareBean bean = (ContextAwareBean) factory.getBean("ContextAwareBean");
        bean.process();
        */
        //ContextAwareBean 只能从ApplicationContext获得bean
        //ContextAwareBean bean = (ContextAwareBean) ctx.getBean("ContextAwareBean");
        //bean.process();
                
        ReplacedBean bean1 = (ReplacedBean) factory.getBean("ReplacedBean");
        bean1.process();
    }
}
*对于实现ApplicationContextAware的Bean,必须用 ApplicationContext的getBean方法.对于方法注入( lookup-method方式):用BeanFactory和ApplicationContext的getBean都可以.如果要用BeanFactory,应该实现BeanFactoryAware:
public class BeanFactoryAwareBean implements BeanFactoryAware {
    protected static final Log log = LogFactory.getLog(BeanFactoryAwareBean.class);
    private String anotherBeanName;
   
    private BeanFactory beanFactory;
   
    public String getAnotherBeanName() {
        return anotherBeanName;
    }
    public void setAnotherBeanName(String anotherBeanName) {
        this.anotherBeanName = anotherBeanName;
    }
    public void process() {
        log.info("process beanFactory " + beanFactory);
        AnotherBean anotherBean = createAnotheBean();
        anotherBean.doSth();      
    }
    protected AnotherBean createAnotheBean() {
   
    return this.beanFactory.getBean(anotherBeanName, AnotherBean.class);
    }
   
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;       
    }
}
两种方法的比较:理论上来讲,第二种方法更体现了IoC的思想,而且在bean类里面没有依赖到Spring,只是一个POJO.客户端在使用它的时候可以是依靠Spring配置(lookup-method)来使用,也可以通过提供实现类来完成调用.
原文链接:http://blog.csdn.net/kkdelta/article/details/5476423
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